In fact, the second sensor will be sensitive to measuring the water level in the tank. The first sensor is a selector for on/off operation, and the output will be the motor for drawing water from the tank.
The requirement is to activate the water motor when there is water in the tank. If there is no water in the tank, the motor will not be activated.
if you just connect with a switch push to simulate water tank level sensor. OK, which type of water level sensor you have used? analog 0-5v sensor or a float switch water level sensor(it output digital signal) ?